The effect of pressure on the aluminoborosilicate glass optical basicity

Abstract

The glass optical basicity (Λ) is an adequate way of representing a glass composition that has been successfully applied for glasses made under ambient pressure conditions. However, we do not know if the proposed calculation based on the glass structure and the proposed measurement involving the determination of glass refractive index can apply to glasses made under high-pressure conditions. We studied several aluminoborosilicate glass compositions synthesized under high-pressure conditions up to 3 GPa and 1250°C. Recovered glasses were characterized to determine the refractive index (n_D) and the density (ρ). The glass structure was determined using ¹¹B and ²⁷Al nuclear magnetic resonance. Increasing pressure up to 3 GPa increases n_D and ρ for the studied glasses. Change in the glass structure is consistent with previous studies showing an increase in Al coordination, especially for Ca-bearing glass composition; and an increase in the proportion of BO₄ species. The glass optical basicity decreases with increasing pressure. From the structural changes, Λ decreases by ∼2% from ambient to 1 GPa in pressure for the investigated glass compositions.